Systems and methods for assessing vasculature health and blood clots

ABSTRACT

A system and method for determining a pH level of blood in a vessel of a patient including a flexible elongated member configured and dimensioned for insertion in the vessel of the patient, a sensor positioned at the distal portion of the elongated member, and a connector connecting the elongated member to an indicator. The sensor measures the pH level of blood downstream of the blood clot. A system and method are also provided for determining a density of a blood clot in a vessel of a patient for subsequent selection of a treatment method. The system includes a sensor positioned at the distal portion of the elongated member, and a connector connecting the elongated member to an indicator, wherein the sensor determines the density of the blood clot and the indicator provides an indication of the density of the clot.

This application claims priority from provisional application Ser. No.61/718,107, filed Oct. 24, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND

1. Technical Field

This application relates to a system for determining the health of thevasculature to enable the surgeon to assess the advisability of bloodclot removal. This application also relates to a system for identifyingthe composition of a blood clot in a vessel to enable the physician toscientifically determine the clot makeup to determine the best course oftreatment for the clot.

2. Background of Related Art

Cerebrovascular disease refers to diseases of the brain caused byvascular abnormalities which result in abnormal cerebral blood flow. Themost common cause of cerebrovascular disease is narrowing of the majorarteries supplying blood to the brain, resulting in thrombogenic diseaseor sudden occlusion of blood flow, which if large enough results inischemic stroke.

Clots (Ischemic Stroke) can originate in various areas and be caused bydifferent modalities. These different modalities create clots that varyin consistency. The clot can be platelet rich (runny) or fibrin rich(hard) or anywhere in between the two. Ischemic stroke is caused by thethrombosis of a major vessel supplying blood to a region of the brain. Ashortage of blood in the cerebral tissue leads to the deletion ofmetabolites such as oxygen and glucose, which in turn causes depletionof energy stores of the cells. Therefore, it is critical to remove theclots to restore adequate blood supply to the brain.

Current treatments for clot removal include mechanical thrombectomydevices and application of thrombolytic drugs to dissolve the clot. Aproblem encountered with these approaches is that the composition of theclot is undetectable in situ, while the efficacy of these approaches isdependent in part on the clot composition. Therefore, the physician istaking one of the known approaches for treatment of the clot without theknowledge of the clot makeup, e.g., its consistency. This can lead toinconsistent results as well as failure to properly treat the clot.

It would therefore be beneficial if the surgeon could identify the typeof clot beforehand to better assess how the clot could be treated. Suchprior knowledge would greatly enhance clot removal as the surgeon canadapt the approach to better match the treatment device or drugs withthe type of clot.

In addition, in cerebrovascular disease, the vitality of the vasculaturedistal to the clot is compromised once the clot lodges in place.Vasculature that has been deprived of oxygenated blood will necrose andbecome friable. Once blood flow is restored after clot removal, suchblood flow could potentially cause a hemorrhagic event, which means thevessel can bleed out and burst open. Currently, surgeons do not haveadequate knowledge of the vasculature downstream of the clot andtherefore cannot accurately assess the risk of clot removal.

It would be beneficial if the surgeon could determine the health of thevasculature distal to the clot prior to removal of the clot so thesurgeon could determine if clot removal is advisable and/or takenecessary precautions during clot removal so the vessels are notcompromised. Prior attempts to measure pH using magnetic resonanceimaging (MRI) technique have been attempted, as explained for example in“Modelling of pH Dynamics in Brain Cells After Stroke”, by PiotrOrlowski, et al., published in Interface Focus, The Royal Society, 2011.However, these attempts to date have been unsuccessful. Additionally,relying on MRI is very expensive and requires relatively complexmathematical models. Therefore, although the role of pH is recognized,the need exists to utilize this parameter to readily determine vasculartissue health to enhance blood clot removal or prevent clot removalwhere the risk is too great.

SUMMARY OF THE INVENTION

The present invention provides a system and method for assessingvasculature downstream of the clot and a system and method for assessingthe blood clot. The two systems can be used independently, oralternatively, can be used together as either separate systems or asingle (combined) system.

In one aspect, the present invention provides a system for determining apH level of blood in a vessel of a patient. The system comprises aflexible elongated member configured and dimensioned for insertion inthe vessel of the patient, the elongated member having a proximalportion and a distal portion and configured for insertion so the distalportion extends past a blood clot for positioning of the distal portiondistal of the blood clot. A sensor is positioned at the distal portionof the elongated member for positioning distal of the blood clot. Aconnector connects the elongated member to an indicator, the sensormeasuring the pH level of blood, preferably in a closed or asubstantially closed system downstream of the blood clot, to therebydetermine pH of the vessel downstream of the blood clot to determine thecondition of the vessel to assess subsequent treatment of the bloodclot. The indicator provides an indication of the blood pH measured bythe sensor.

In one embodiment, the flexible elongated member comprises a catheter.In another embodiment, the flexible elongated member comprises aguidewire.

In one embodiment, the sensor is embedded in a wall of the elongatedmember. In another embodiment, the sensor is positioned on an outersurface of the elongated member.

The system can include in some embodiments a second sensor for sensing aparameter of the blood clot and a second indicator to indicate thesensed parameter, the second sensor connected to the second indicator.In some embodiments, the second sensor senses a density of the bloodclot. In some embodiments, the second sensor is positioned on a secondelongated member coaxial with the elongated member carrying the sensorfor measuring pH. In some embodiments, the second sensor is proximal ofthe first sensor.

In accordance with another aspect, the present invention provides amethod for determining a pH level of blood downstream of a blood clot ina vessel of a patient comprising the steps of:

-   -   providing an elongated flexible member;    -   inserting the flexible member through vasculature of the patient        and past the blood clot to a position downstream of the blood        clot in the vessel;    -   sensing a pH level of the blood downstream of the clot; and    -   indicating to the user the pH level of the blood to enable the        user to determine a pH level of the vessel downstream of the        blood clot for subsequent selection of a clot treatment        approach.

In some embodiments, the method further comprises the step ofdetermining a density of the blood clot to determine a clot treatmentmethod. In some embodiments, the step of determining the density of theblood clot utilizes a sensor proximal of a sensor used for sensing pH ofthe blood. In some embodiments, one of the density sensor and pH sensoris on a first elongated flexible member and the other sensor is on asecond elongated flexible member coaxial with the first elongatedmember.

In accordance with another aspect, the present invention provides asystem for determining an oxygen level of blood in a vessel of apatient. The system comprises a flexible elongated member configured anddimensioned for insertion in the vessel of the patient, the elongatedmember having a proximal portion and a distal portion and configured forinsertion so the distal portion extends past a blood clot forpositioning of the distal portion distal of the blood clot. A sensor ispositioned at the distal portion of the elongated member for positioningdistal of the blood clot. A connector connects the elongated member toan indicator, the sensor measuring the oxygen level of blood, preferablyin a closed or a substantially closed system downstream of the bloodclot, to thereby determine the oxygen level of the vessel downstream ofthe blood clot to determine the condition of the vessel to assesssubsequent treatment of the blood clot. The indicator provides anindication of the oxygen level of the blood measured by the sensor.

In accordance with another aspect, the present invention provides amethod for determining an oxygen level of blood downstream of a bloodclot in a vessel of a patient comprising the steps of:

-   -   providing an elongated flexible member;    -   inserting the flexible member through vasculature of the patient        and past the blood clot to a position downstream of the blood        clot in the vessel;    -   sensing an oxygen level of the blood downstream of the clot; and    -   indicating to the user the oxygen level of the blood to enable        the user to determine an oxygen level of the vessel downstream        of the blood clot for subsequent selection of a clot treatment        approach.

In accordance with another aspect of the present invention, a system fordetermining a density of a blood clot in a vessel of a patient forsubsequent selection of a treatment method is provided. The systemcomprises a flexible elongated member configured and dimensioned forinsertion in the vessel of the patient, the elongated member having aproximal portion and a distal portion and the distal portion configuredfor insertion adjacent the blood clot. A sensor is positioned at thedistal portion of the elongated member. A connector connects theelongated member to an indicator, the sensor determining the density ofthe blood clot and the indicator providing an indication of thedetermined density.

In one embodiment, the flexible elongated member comprises a catheter.In another embodiment, the flexible elongated member comprises aguidewire.

The system in some embodiments further comprises a transmitter at thedistal portion of the elongated member for transmitting ultrasonic wavestoward the blood clot, and the density of the blood clot is determinedby ultrasonic wave feedback. The system in some embodiments can furtherinclude a pH sensor for measuring pH of blood downstream of the clot andan indicator for indicating measured pH.

The present invention provides in another aspect a method fordetermining a density of a blood clot in a vessel of a patient forsubsequent selection of a clot treatment method. The method comprises:

-   -   providing a flexible elongated member configured and dimensioned        for insertion in the vessel of the patient, the elongated member        having a proximal portion and a distal portion, the elongated        member distal portion configured for insertion adjacent a blood        clot;    -   transmitting ultrasonic waves toward the blood clot; and    -   determining the density of the blood clot based on the        ultrasonic wave feedback.

In some embodiments, the method further provides a visual indication ofthe determined density.

In some embodiments, the method further includes positioning theelongated member so that a distal tip extends past the blood clot and adensity sensor is positioned proximal of the distal tip within the bloodclot.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present disclosure are described hereinwith reference to the drawings wherein:

FIG. 1 is a side view of a first embodiment of the system of the presentinvention illustrating a catheter coupled to a pH reader and showing thecatheter tip positioned distal of the blood clot;

FIG. 2A is a close up perspective view of the pH reader of FIG. 1;

FIG. 2B is a close up perspective view of an oxygen level reader;

FIG. 3A is a close up view of the catheter tip of FIG. 1 showing the pHsensor on an outer surface of the catheter for determining blood pH;

FIG. 3B is a close up view of the catheter tip showing the pH sensorembedded in the wall of the catheter in accordance with an alternateembodiment;

FIG. 4 is a close up perspective of the coupler of FIG. 1 for connectingthe pH reader cable to the catheter;

FIG. 5 is a close up view of the vasculature illustrating the cathetertip of FIG. 1 positioned past a blood clot;

FIG. 6 is a side view of an alternate embodiment of the system of thepresent invention illustrating a guidewire coupled to a pH reader andshowing the guidewire positioned distal of the blood clot;

FIG. 7 is a close up perspective view of the coupler connecting the pHreader cable to the guidewire;

FIG. 8A is a close up view of the guidewire of FIG. 6 positioned distalof the clot and showing the pH sensor on the outer tip of the guidewire;

FIG. 8B is a cutaway view showing the pH sensor embedded in the wall ofthe guidewire in accordance with an alternate embodiment;

FIG. 8C is a close up view of an alternate embodiment having a densitysensor spaced from the distal tip;

FIG. 9A is side view of an alternate system of the present inventionillustrating a catheter coupled to a density reader and showing thecatheter tip positioned distal of the blood clot;

FIG. 9B is a close up view of the distal portion of the catheter of FIG.9A showing the density sensor within the clot;

FIG. 10 is a close up view of the density reader of FIG. 9A showing aclot density reading;

FIG. 11A is a side view of an alternate embodiment of the system of thepresent invention illustrating a guidewire coupled to a density readerand showing the guidewire positioned distal of the blood clot;

FIG. 11B is a close up view of the distal portion of the guidewire ofFIG. 11A, with the clot broken away to show the density sensor withinthe clot;

FIG. 12A is a side view of another alternate system of the presentinvention showing a catheter coupled to a pH reader and a guidewirecoupled to a density reader, and further showing the catheter tip andguidewire positioned distal of the blood clot;

FIG. 12B is a close up view of the distal end of the catheter andguidewire of FIG. 12A, showing retraction of the catheter to expose thedensity sensor on the guidewire; and

FIG. 13 is an enlarged view of the density reader of FIG. 12A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a system for determining the health orcondition of the vasculature distal of the blood clot. This aids thephysician in assessing the effect of removal of the blood clot from thevessel. The present invention also provides a system for determining thetype of blood clot. This enables the physician to assess the best modeof treatment of the blood clot. These two systems can be usedindependently or alternatively can be used together. That is, it iscontemplated that only one of the systems is utilized so the usermeasures only one of the parameters, i.e., either health of vasculatureor type of clot. However, it is also contemplated that both systems beutilized so the user can determine both parameters. These systems aredescribed in detail below.

Vasculature Determination

Turning first to the system for determining the health or condition ofthe vasculature, this system is illustrated in FIGS. 1-8, with FIGS. 1-5illustrating an embodiment where the pH sensor is located on a catheterand FIGS. 6-8B illustrating an embodiment where the pH sensor is locatedon a guidewire. It is also contemplated that a pH sensor can bepositioned on the catheter and on the guidewire, and it is alsocontemplated that one or more pH sensors can be positioned on thecatheter and one or more pH sensors can be positioned on the guidewire.Multiple sensors would enable different regions of the blood (andtherefore the vasculature) to be measured. In certain embodimentsutilizing multiple pH sensors, the sensors can be spaced apartsufficiently so that a pH measurement can be taken both upstream anddownstream of the blood clot for comparative purposes in assessingvasculature health.

The system for measuring pH is beneficial since in certain instances,the vitality of the vasculature distal to the clot is compromised oncethe clot lodges in place. Vasculature that has been deprived ofoxygenated blood will necrose and become friable. Once blood flow isrestored after clot removal, such blood flow could potentially cause ahemorrhagic event, which means the vessel can bleed out and burst open.Therefore, this system provides a way of determining the health of thevasculature distal to the clot so the physician could determine if clotremoval is advisable or take other precautions during clot removal. Thatis, the physician will be able to determine if the clot should beremoved based upon the pH content of the vasculature distal to the clot.

Such determination can be done measuring pH. It could also beaccomplished in an alternate embodiment by sensing oxygen levels in theblood which would provide an indication of the health of thevasculature. Other parameters could also be measured.

With respect to pH, it is understood that intracellular pH is importantin the maintenance of normal cell function. Blood pH is regulated by asystem of buffers that continuously maintain its normal range of 7.35 to7.45. Blood pH drop below 7 or above 7.45 can cause serious problems,including death. Studies have shown that carbon dioxide plays a vitalrole in blood pH abnormality. Carbon dioxide serves as a buffer. Ascarbon dioxide becomes depleted, the pH drops and acidosis and/orapoptosis occurs.

With the presence of a blood clot, there is essentially a closed system(or substantially closed system) created in the vasculature since bloodflow downstream of the clot has mostly stopped. Being a closed system,the pH of the blood can be measured and the blood pH will be indicativeof the pH of the adjacent vasculature. Thus, the measurement of theblood pH as described herein provides an inexpensive, accurate andeffective way to determine the pH and thus the health of the adjacentvasculature. The pH can be measured utilizing known techniques such asan ionic potential sensor that converts the activity of a specific iondissolved in a solution into an electric potential which can bemeasured. Known glass and crystalline membranes can be utilized.

It is also contemplated that instead of measuring blood pH, the oxygenlevel of the blood can be measured downstream of the blood clot,preferably in a closed or substantially closed system, to therebydetermine the health of the vasculature.

Turning more specifically to the system of FIGS. 1-5, catheter 10 has aproximal portion 12 and a distal portion 14. The catheter tube 16 issufficiently flexible to navigate the small vessels while having somerigidity to enable it to be directed around the curves of thevasculature. An RHV (rotating hemostatic valve) 20 is attached to thecatheter hub 22 and includes a side arm 24 for fluid injection and/oraspiration. Coupler (connector) 30 is attached to the catheter 10, andis connected to cable 34 which is connected to pH reader (meter) 40. Inone embodiment, as shown in FIG. 4, the coupler 30 is u-shaped withopening 31 between the legs of the “u” dimensioned to frictionally clamponto the outer wall of the catheter 10. That is, the coupler 30 is shownin the embodiment of FIG. 1 in the form of a U-shaped clip with theradius of the U smaller than that of the outer wall of the catheter soit flexes outwardly when placed over the strain relief of the catheterand then is frictionally retained on the catheter. In anotherembodiment, a second connector (coupler) half is placed opposite theconnector to form a 360 degree clip or clamp surrounding the outer wallof the catheter to retain the connector on the catheter 10. Othermethods of attachment are also contemplated such as magneticattachments. Cable 34 is connected to the coupler at one end 35 andconnected at the opposing end 36 to reader 40. As shown (FIG. 1), thecoupler 30 is attached to the region of catheter 10 just distal of hub22, although other locations are also contemplated. The coupler 30 canbe attached to the strain relief of the catheter 10 to enhance coupling.

The pH sensor 26 for measuring blood pH is positioned at the distalportion 14 of the catheter 10 and is electrically coupled to cable 34via a pair of wires (not shown) extending from the sensor 26 to thecoupler 30 and/or cable 34. The wires can be embedded in a wall of thecatheter 10 or alternatively extend through a lumen in the catheter 10.In the embodiment of FIG. 3A the sensor 26 is positioned on an outerwall of the catheter 10, extending circumferentially around 360 degrees.The sensor can also be incorporated into a marker band at the tip of thecatheter 10. In the alternate embodiment of FIG. 3B, the sensor 26′ ispositioned inside the catheter 10, either internal of the inner catheterwall or alternatively embedded in the wall of the catheter 10′. Wires 27connect the sensor 26′ to the conductor 30 and/or cable 24, with twolines coming into the reader 40 with two lines extending to the sensor26.

The pH reader 40 provides an indicator device and contains an on offswitch 42. A reading 44 provides a visual indication, as a numericvalue, of the measured pH of the blood to inform the user of the pH ofthe blood, and therefore the vasculature. FIG. 2 shows by way of examplea reading of 6.4 which is below the normal range of 7.35 to 7.45 andthus indicates acidosis has likely occurred which affects (compromises)the vasculature structure.

In use, the catheter 10 (or 10′) can be inserted utilizing knownmethods, e.g., through a femoral approach or a brachial approach, andadvanced through the vascular system to the desired treatment site, e.g.a cerebral artery A. The catheter tip 11 is advanced past the blood clotC (see e.g., FIG. 5). The sensor is activated to measure pH, with the pHreader turned on so that pH value can be determined. As noted above, theclosed system advantageously enables the user to determine thevasculature condition by measuring the blood pH rather than the pH ofthe vasculature itself. Proper treatment approaches, e.g., decidingwhether the clot can be safely removed or taking other precautions toprotect the vessel, can then be implemented.

FIGS. 6-8B illustrate an alternate embodiment for measuring pH utilizinga sensor on a guidewire instead of the catheter as in FIG. 1. In thisembodiment, guidewire 50 has a proximal portion 52 and a distal portion54. The guidewire 50 is sufficiently rigid to navigate the small vesselswhile having some rigidity to enable it to be directed around the curvesof the vasculature. In one embodiment the guidewire is hollow and thewire runs through the lumen from the sensor to the connector, and thewire, as in other embodiments herein, is preferably insulated. Inanother embodiment, the guidewire is a solid core and a polymeric jacketcontains the insulated wire on an outer surface of the guidewire. Theguidewire is illustrated within a lumen of a catheter 70 having a RHV 74attached to the proximal end. The RHV 74 is attached to the hub 72 ofthe catheter 70 and includes a side arm 75 for injection and/oraspiration. Coupler 80 is attached to the guidewire 50, and is connectedto cable 83 which is connected to pH reader 40. The pH reader can be thesame as in the embodiment of FIG. 1. In one embodiment, as shown in FIG.7, the coupler (connector) 80 is u-shaped with opening 81 between thelegs of the “u” dimensioned to frictionally clamp onto the outer wall ofthe guidewire 50. A two part connector as described above could also beutilized. Other methods of attachment are also contemplated includingmagnetic attachments for example. Cable 83 is connected to the coupler80 at one end 85 and connected at the opposing end 86 to reader 40.

The pH sensor 56 is positioned at a distal end of the guidewire 50 andis electrically coupled to coupler 80 and/or cable 84 via a pair ofwires (not shown) extending from the sensor 56. The wires can beembedded in a wall of the guidewire 50 or alternatively the guidewirecan have a lumen or channel through which the wires extend. In theembodiment of FIG. 8A, the sensor 56 is positioned on an outer wall ofthe guidewire 50, extending circumferentially around 360 degrees. Thesensor can also be incorporated into a marker band at the tip of theguidewire 50. In an alternate embodiment, the sensor 56′ and wires 57(only one is shown) of guidewire 50′ can be positioned inside theguidewire 50′, either internal of the inner wall of the guidewire asshown in FIG. 8B, or alternatively embedded in the wall of theguidewire. The catheter 70 through which the guidewire extends can havea marker band 79. Note in FIG. 8A, the catheter 70 and guidewire 50 arepositioned in a cerebral artery A distal of clot C.

In use, the switch 42 of the pH reader 40 is activated and the sensor 56is activated to measure the blood pH and the pH reader provides anumeric pH value of the blood. FIG. 6 shows a pH reading of 6.4 by wayof example. Note the guidewire 50 can be inserted utilizing knownmethods, e.g., through a femoral approach or a brachial approach, andadvanced through the vascular system to the desired treatment site, e.g.the cerebral artery. In a preferred method, first an introducer isplaced in the femoral artery, and a large guidewire and guide catheteris advanced to the carotid artery. The large guidewire is removed, andreplaced with a microcatheter 70 and a smaller dimensioned guidewire 50of the present invention which contains sensor 56. The catheter tip 71(containing maker band 79 for imaging) and guidewire tip 51 are advancedpast the blood clot C (see e.g., FIG. 8A). The sensor 56 measures the pHand transmits the measurement through the wires extending in guidewire50 back to the cable 83 which in turn transmits it to the reader 40. Asnoted above, the closed system advantageously enables the user todetermine the vasculature condition by measuring the blood pH ratherthan the pH of the vasculature (or surrounding tissue) itself. Propertreatment approaches for the treating the blood clot can then be betterselected. That is, the physician can determine whether removal of theclot would be too traumatic to the vessel and risk hemorrhaging.

Note the sensors are shown at the distalmost tip of the catheter (FIGS.1-5) or guidewire (FIGS. 6-8B) but alternatively can be spaced proximalof the distalmost tip such as the sensor 56 a of guidewire 50 a of FIG.8C.

The pH sensors can be used in other applications such as in cases ofgangrene or tissue dying for some other reason to intravascularly assessthe vasculature or health of the tissue.

In an alternate embodiment, the oxygen level of the blood can bemeasured which is indicative of the oxygen and thus the health of thevasculature. The system would be the same as with the above describedsystems, except one or more oxygen sensors (rather than pH sensors)would be provided on the catheter or the guidewire and connected to anoxygen reader (meter) such as shown in FIG. 2B. The oxygen readerprovides an indicator of the oxygen level, by providing for example anumeric value, or other indicator, to indicate a range of low to highoxygen level measurements. The sensors can be positioned on the catheteror guidewire in the similar manners of the pH sensors disclosed herein.

Clot Determination

As noted above, the present disclosure provides a system to identify aparameter such as the composition of a clot in a vessel which willenable the physician to scientifically determine the clot makeup anddetermine the best course of treatment from the available tool sets.This can be achieved in accordance with one embodiment using ultrasound.

More specifically, in the embodiment utilizing ultrasonic waves, thedensity of the clot can be estimated, in vivo, by determining the timeit takes for an ultrasonic sound wave to “bounce” back from the clot.The longer the signal takes to return, the less dense the clot is. Thatis, an ultrasound signal will return more quickly when interacting witha denser substrate. The average densities of traditional “soft” clot ornormal clot and the denser fibrin clot is determined to providepredetermined parameters, and then the system of the present disclosurecompares the signal generated by the ultrasonic wave to these parametersto inform the physician of the type of clot. Thus, the system utilizes alogic circuit to determine the makeup of the clot quickly, efficientlyand effectively. By way of example, a soft clot can be assigned anumeral 1 and a hard clot assigned a numeral 10, and the clot densitymeasured to assign a value within this range so the physician wouldfirst be informed of the type of clot before taking treatment steps,such as removal of the clot. In other words, the measured averagedensities of both normal clot and fibrin will provide a “baseline”incorporated into the logic-circuit which will determine, in vivo duringthe surgical procedure, which clot type is present within the vessel.Other numeric values or indicators are also contemplated to indicatevarying densities.

To generate and provide a digital or analog readout of these ultrasoundsignals a piezoelectric signal transducer can be used. Piezoelectricmaterials are crystalline structures which undergo a mechanicaldeformation when a certain voltage is applied to the crystal. Thisproperty is used in conjunction with an applied AC voltage applied tothe crystal. As the AC voltage is applied to the piezo-material it willdeform and generate a sound wave. Likewise, when a mechanical load isplaced on the piezoelectric crystal a small voltage is generated. Thisproperty is used to convert an ultrasonic signal into a measurablevoltage. The piezoelectric crystal has a specific voltage/frequencyrelationship which can be used to convert between the two.

Because of these unique properties, the same piezoelectric transducerwhich generates an ultrasonic signal can also be used to receive thereflected signal returning from a substrate. Utilizing these propertiesthe ΔT (change in time) can be determined between the sent signal andthe received signal by having predetermined the average ΔT for bothnormal and fibrin clots; the designed logic circuit will be able todetermine which clot is present.

This ultrasonic signal is sent from within the vasculature to ensurethat interference from cranial tissues, muscle, bone, etc. do not affectmeasurements. The size and shape of the piezoelectric crystal willdetermine the distance at which the measurement can be best made.

Turning now to the system of FIGS. 9A-12B, a system for determining thetype of clot is illustrated, with FIG. 9 illustrating an embodimentwhere the density sensor (utilizing ultrasound as described above) is ona catheter and FIG. 11 illustrating an embodiment where the densitysensor (utilizing ultrasound) is on a guidewire. It is also contemplatedthat a density sensor can be positioned on the catheter and on theguidewire, and it is also contemplated that one or more density sensorscan be positioned on the catheter and one or more density sensorspositioned on the guidewire. This enables more than one region of theclot to be measured which could be beneficial in large clots.

Turning more specifically to the system of FIGS. 9A, 9B and 10, catheter110 has a proximal portion 112 and a distal portion 114. The cathetertube 116 is sufficiently flexible to navigate the small vessels whilehaving some rigidity to enable it to be directed around the curves ofthe vasculature. An RHV 120 is attached to the catheter hub 122 andincludes a side arm 124 for fluid injection and/or aspiration. Coupler130 is attached to the catheter 110, and is connected to cable 134 whichis connected to density reader (meter) 140. In one embodiment, thecoupler 130 can be the same as coupler 30 of the embodiment of FIG. 1and can be u-shaped with an opening between the legs of the “u”dimensioned to frictionally clamp onto the outer wall of the catheter110. That is, the coupler can be in the form of a U-shaped clip with theradius of the U smaller than that of the outer wall of the catheter soit flexes outwardly when placed over the strain relief of the catheterand then is frictionally retained on the catheter. In anotherembodiment, a second connector half is placed opposite the connector toform a 360 degree clip or clamp surrounding the outer wall of thecatheter to retain the connector (coupler) on the catheter 110. Othermethods of attachment are also contemplated such as magneticattachments. A cable 134 is connected to the coupler at one end 135 andconnected at the opposing end 136 to density reader 140. As shown, thecoupler 130 is attached to the region of catheter 110 just distal of hub122, although other locations are also contemplated.

The density sensor 126 is positioned at the distal portion 114 of thecatheter 110, at the distalmost tip 115 and is electrically coupled tocable 134 via a pair of wires (not shown) extending from the sensor 126to the coupler 130 and/or cable 134. The wires can be embedded in a wallof the catheter 110 or alternatively extend through a lumen in thecatheter 110. The sensor 126 in the illustrated embodiment is at thedistalmost tip but alternatively could be spaced from the distalmost endso the catheter tip can extend past the clot during use while the sensoris positioned within the clot. The sensor can be positioned on an outerwall of the catheter 110, extending circumferentially around 360degrees. The sensor can also be positioned inside the catheter 110,either internal of the inner catheter wall or alternatively embedded inthe wall of the catheter. Wires (not shown) connect the sensor to thecoupler 130 and/or cable 124.

The density reader 140 provides an indicator device and contains an onoff switch 142. A reading 144 provides a visual indication as a numericvalue representative of a comparative density as explained above. FIG.10 shows a density reading of “5” by way of example, indicating a clotdensity midway between the outer soft clot and outer hard clot range.Connector (coupler 120) is wired to the reader 140 which provides areading of the clot type based on the signal received from the sensor126 in response to the ultrasonic signal caused by the ultrasonic wavesapplied to the clot. In use, the catheter 110 can be inserted utilizingknown methods, e.g., through a femoral approach or a brachial approach,and advanced through the vascular system to the desired treatment site,e.g. the cerebral artery A. The catheter tip 115 is advanced past theblood clot C (see e.g., FIG. 9B) so the sensor 126 is located within theblood clot. The sensor 126 is activated, using ultrasonic waves tomeasure density, with the density reader providing a visual densityindication so the user can decide the optimal way to treat the clot.

FIG. 11A illustrates an alternate embodiment for measuring densityutilizing a sensor on a guidewire instead of the catheter as in FIG. 9A.In this embodiment, guidewire 150 has a proximal portion 152 and adistal portion 154. The guidewire 150 is sufficiently rigid to navigatethe small vessels while having some rigidity to enable it to be directedaround the curves of the vasculature. In one embodiment, the guidewireis hollow and the wires run through the lumen from the sensor to theconnector, and the wires are preferably insulated. In anotherembodiment, the guidewire is a solid core and a polymeric jacketcontains the insulated wires on an outer surface of the guidewire. Theguidewire is illustrated within a lumen of a catheter 170 having a RHV174 attached to the proximal end. The RHV 174 is attached to the hub 172of catheter 170 and includes a side arm 175 for injection and/oraspiration. Coupler 180 is attached to the guidewire 150, and isconnected to cable 183 which is connected to density reader 140. Thedensity reader 140 can be the same as in the embodiment of FIG. 10. Inone embodiment, the coupler is the same as coupler 80 of FIG. 7 and isu-shaped with an opening in the “u” dimensioned to frictionally clamponto the wall of the guidewire 150. A two part connector (coupler) asdescribed above can also be utilized. Other methods of attachment arealso contemplated such as magnetic attachments. Cable 183 is connectedto the coupler 180 at one end 185 and connected at the opposing end 186to meter 140.

Density sensor 156 is positioned at a distal end of the guidewire 150,either at the distalmost tip or spaced from the distalmost tip as shownin FIG. 11B, and is electrically coupled to coupler 180 and/or cable 184via a pair of wires (not shown) extending from the sensor 156. The wirescan be embedded in a wall of the guidewire 150 or alternatively theguidewire can have a lumen or channel through which the wires extend. Inthe embodiment of FIGS. 11A and 11B the sensor 156 is positioned on anouter wall of the guidewire 150, extending circumferentially around 360degrees. The sensor can also be incorporated into a marker band at thetip of the guidewire 150. In an alternate embodiment, the sensor can bepositioned inside the guidewire 150, either internal of the inner wallof the guidewire in the same manner as in the embodiment of FIG. 8B, oralternatively embedded in the wall of the guidewire. The catheter 170through which the guidewire extends can have a marker band. Note in FIG.11A, the guidewire 150 is positioned with the sensor in the clot C andthe catheter 170 is positioned in a cerebral artery A proximal of clotC.

In use, the density sensor 156 is activated to selectively measure thedensity of the blood clot and with switch 42 turned on, densityindication is provided. Note the guidewire 150 can be inserted utilizingknown methods, e.g., through a femoral approach or a brachial approach,and advanced through the vascular system to the desired treatment site,e.g. the cerebral artery. In a preferred method, first an introducer isplaced in the femoral artery, and a large guidewire and guide catheterare advanced to the carotid artery. The large guidewire is removed, andreplaced with a microcatheter 170 and a smaller dimensioned guidewire150 of the present invention which contains sensor 156. The catheter tip171 is advanced past the blood clot C. The guidewire 150 is positionedin the clot and in some embodiments the catheter 170 is withdrawnproximally to expose the sensor 156 within the clot C to measure thedensity of the clot and transmit the measurement through the wiresextending in guidewire 150 back to the cable 183 which in turn transmitsit to the reader 140. Proper treatment approaches for the treating theblood clot can then be better be selected. That is, the reader 140 isused to indicate density measurement so the physician can determine theoptimal way to treat the clot.

Combination of Systems

It is contemplated that the system for determining clot density (orother clot parameter) and the system for measuring the blood pH (orother blood parameter such as oxygen) can be used together. In suchsystem, both the density sensor and pH sensor (or oxygen sensor) alongwith a density and pH (or oxygen) reader are provided. Such system isshown in the embodiment of FIGS. 12A-13.

Catheter 210 has a proximal portion 212 and a distal portion 214. Thecatheter tube 216 is sufficiently flexible to navigate the small vesselswhile having some rigidity to enable it to be directed around the curvesof the vasculature. An RHV 220 is attached to the catheter hub 222 andincludes a side arm 224 for fluid injection and/or aspiration. Coupler230 is attached to the catheter 210, and is connected to cable 234 whichis connected to pH reader (meter) 241 of reader 240. Reader 240 providesboth a pH reading and a density reading. Although shown as a singlereader (meter), it is also contemplated that separate meters, such as inFIGS. 2 and 10 could be provided. In one embodiment, the coupler 230 isidentical to the embodiment of FIG. 4, being U-shaped with an opening inthe “u” dimensioned to frictionally clamp onto the outer wall of thecatheter 210. Alternatively, a second connector (coupler) half asdescribed above can be utilized. Other methods of attachment are alsocontemplated. Cable 234 is connected to the coupler 230 at one end 235and connected at the opposing end 236 to reader 241. As shown, thecoupler 230 is attached to the region of catheter 210 just distal of hub222, although other locations are also contemplated.

The pH sensor 226, identical to the sensor of FIG. 1, is positioned atthe distal portion 214 of the catheter 210 and is electrically coupledto cable 234 via a pair of wires (not shown) extending from the sensor226 to the coupler 230 and/or cable 234. The wires can be embedded in awall of the catheter 210 or alternatively extend through a lumen in thecatheter 210. In the embodiment of FIG. 12A, the sensor is positioned onan outer wall of the catheter 210, extending circumferentially around360 degrees in an identical manner as shown in FIG. 3A. The sensor canalso be incorporated into a marker band at the tip of the catheter 210.In the alternate embodiment, the sensor can be is positioned inside thecatheter 210 (similar to sensor 26′ of FIG. 3B), either internal of theinner catheter wall or alternatively embedded in the wall of thecatheter. The pH sensor can be positioned at the distalmost tip as shownor alternatively spaced proximally of the distalmost tip. Wires connectthe sensor 236 to the coupler 230 and/or cable 224.

The pH reader 241 contains an on off switch 248 to selectively provide areadout of the measured pH. A reading 244 provides a visual indication,as a numeric value, of the measured pH of the blood for the user todetermine the pH of the vasculature.

Guidewire 250 has a proximal portion 252 and a distal portion 254. Theguidewire 250 is sufficiently rigid to navigate the small vessels whilehaving some rigidity to enable it to be directed around the curves ofthe vasculature. The guidewire 250 is illustrated within a lumen ofcatheter 210. Coupler 280 is attached to the guidewire 250, and isconnected to cable 283 which is connected to density reader 245 ofreader 240. In one embodiment, the coupler 280 is the same as coupler 80of FIG. 7 and is u-shaped with opening in the “u” dimensioned tofrictionally clamp onto the wall of the guidewire 250. Alternatively, asecond connector (coupler) half as described above can be utilized.Other methods of attachment are also contemplated. Cable 283 isconnected to the coupler 280 at one end 285 and connected at theopposing end 286 to reader (meter) 245.

A density sensor 256, which is identical to sensor 156 of FIG. 11B, ispositioned at a distal portion of the guidewire 250, spaced proximallyof the distalmost tip, and is electrically coupled to coupler 280 and/orcable 283 via a pair of wires (not shown) extending from the sensor. Thewires can be embedded in a wall of the guidewire 250 or alternativelythe guidewire can have a lumen or channel through which the wiresextend. In the embodiment of FIG. 12A, the sensor 256 is positioned onan outer wall of the guidewire 250 in the same manner as sensor 156 ofFIG. 11B, extending circumferentially around 360 degrees. The sensor 256can also be incorporated into a marker band at the tip of the guidewire250. In an alternate embodiment, the sensor can be positioned inside theguidewire 250, either internal of the inner wall of the guidewire in thesame manner as shown in FIG. 8B, or alternatively embedded in the wallof the guidewire. The catheter 210 through which the guidewire 250extends can have a marker band. Note in FIG. 12A, the catheter 210 andguidewire 250 are positioned in a cerebral artery A distal of clot C. Inuse, the catheter 210 can be withdrawn with respect to the guidewire 250to expose the density sensor 256 within the clot as shown in FIG. 12Bwhere the density sensor 256 is proximal of the distal tip. In theembodiment wherein the density sensor 256 is at the distalmost tip, theguidewire 250 would be withdrawn further proximally until the distalmosttip (and sensor) is positioned in the clot.

In the embodiment where the pH sensor is on the guidewire (as in theembodiment of FIG. 6) and the density sensor is on the catheter (as inthe embodiment of FIG. 9A), the catheter need not be withdrawn. Thedensity sensor 256 can be positioned proximal of the pH sensor 226during use since the density sensor is exposed on the outside of thecatheter to measure the blood clot parameter and the pH sensor isexposed on the guidewire to measure the blood parameter downstream ofthe blood clot. In use, the density sensor is activated to measure clotdensity and switch 247 of the density reader 245 of reader 240 is turnedon to provide a visual numeric indication of a relative density. The pHsensor is activated either simultaneously, or at a different time, so pHreader 241 provides a visual numeric indication of blood pH.

It is also contemplated that in some embodiments a pH sensor (or oxygensensor) and a density sensor can both be positioned on a singleguidewire or a single catheter.

Note the guidewire 250 can be inserted utilizing known methods, e.g.,through a femoral approach or a brachial approach, and advanced throughthe vascular system to the desired treatment site, e.g., the cerebralartery. In one method, first an introducer would be placed in thefemoral artery, and a large guidewire and guide catheter would beadvanced to the carotid artery. The large guidewire is removed, andreplaced with a microcatheter 210 which contains a pH (or oxygen) sensor(or alternatively a density sensor), and a smaller dimensioned guidewire250 of the present invention which contains sensor 256. The catheter tip271 is advanced past the blood clot C. The sensor 256 of guidewire 250is positioned in the clot so the sensor measures the density of the clotand transmits the measurement through the wires extending in guidewire250 back to the cable 283 which in turn transmits it to the densityreader 245 of reader 240. (In the embodiment where the catheter containsthe density sensor, the guidewire can contain the pH (or oxygen)sensor). The pH sensor 226 is positioned distal (downstream) of theblood clot to measure pH of the blood distal of the clot and transmit itvia wires to the cable and pH reader 241. As noted above, the closed (orsubstantially closed) system advantageously enables the user todetermine the vasculature condition by measuring the blood pH ratherthan the pH of the vasculature (and surrounding tissue) itself. Propertreatment approaches for the treating the blood clot can be betterselected. The density reading provides information on the blood clotitself. As noted above, an oxygen sensor can be used in the closed orsubstantially closed system to determine the vasculature condition.

While the above description contains many specifics, those specificsshould not be construed as limitations on the scope of the disclosure,but merely as exemplifications of preferred embodiments thereof. Thoseskilled in the art will envision many other possible variations that arewithin the scope and spirit of the disclosure as defined by the claimsappended hereto.

What is claimed:
 1. A system for determining a pH level of blood in avessel of a patient, the system comprising: a flexible elongated memberconfigured and dimensioned for insertion in the vessel of the patient,the elongated member having a proximal portion and a distal portion, theelongated member configured for insertion so the distal portion extendspast a blood clot for positioning of the distal portion distal of theblood clot; a sensor positioned at the distal portion of the elongatedmember for positioning distal of the blood clot; and a connectorconnecting the elongated member to an indicator, the sensor measuringthe pH level of blood downstream of the blood clot to thereby determinepH of the vessel downstream of the blood clot to determine the conditionof the vessel to assess subsequent treatment of the blood clot, theindicator providing an indication of the pH measured by the sensor. 2.The system of claim 1, wherein the flexible elongated member comprises acatheter.
 3. The system of claim 1, wherein the flexible elongatedmember comprises a guidewire.
 4. The system of claim 1, wherein thesensor is embedded in a wall of the elongated member.
 5. The system ofclaim 1, wherein the sensor is positioned on an outer surface of theelongated member.
 6. The system of claim 1, further comprising a secondsensor for sensing a parameter of the blood clot and a second indicatorto indicate the sensed parameter, the second sensor connected to thesecond indicator.
 7. The system of claim 6, wherein the second sensorsenses a density of the blood clot.
 8. The system of claim 7, whereinthe second sensor is positioned on a second elongated member coaxialwith the elongated member carrying the sensor for measuring pH.
 9. Thesystem of claim 8, wherein the second sensor is proximal of the firstsensor.
 10. A method for determining a pH level of blood downstream of ablood clot in a vessel of a patient comprising the steps of: providingan elongated flexible member; inserting the flexible member throughvasculature of the patient and past the blood clot to a positiondownstream of the blood clot in the vessel; sensing a pH level of theblood downstream of the blood clot; and indicating to the user the pHlevel of the blood to enable the user to determine a pH level of thevessel downstream of the blood clot for subsequent selection of a clottreatment method.
 11. The method of claim 10, further comprising thestep of determining a density of the blood clot to determine a clottreatment method.
 12. The method of claim 10, wherein the step ofdetermining the density of the blood clot utilizes a sensor fortransmitting ultrasonic waves.
 13. The method of claim 12, wherein oneof the density sensor and pH sensor is carried by a first elongatedflexible member and the other sensor is carried by a second elongatedflexible member coaxial with the first elongated member.
 14. A systemfor determining a density of a blood clot in a vessel of a patient forsubsequent selection of a treatment method, the system comprising: aflexible elongated member configured and dimensioned for insertion inthe vessel of the patient, the elongated member having a proximalportion and a distal portion, and the elongated member distal portionconfigured for insertion adjacent the blood clot, a sensor positioned atthe distal portion of the elongated member, and a connector connectingthe elongated member to an indicator, the sensor determining the densityof the blood clot and the indicator providing an indication of thedetermined density.
 15. The system of claim 1, wherein the flexibleelongated member comprises a catheter.
 16. The system of claim 1,wherein the flexible elongated member comprises a guidewire.
 17. Thesystem of claim 13, wherein the sensor includes a transmitter at thedistal portion of the elongated member for transmitting ultrasonic wavestoward the blood clot, and the density of the blood clot is determinedby ultrasonic wave feedback.
 18. The method of claim 13, furthercomprising a pH sensor for measuring pH of blood downstream of the clotand an indicator for indicating measured pH.
 19. The method of claim 13,further comprising an oxygen sensor for measuring oxygen level of blooddownstream of the clot and an indicator for indicating measured oxygen.20. The method of claim 19, wherein the density sensor is positionedproximal of the distal tip of the elongated member.